1. Field of the Invention
The present invention relates generally to light emitting diodes, and more particularly to light emitting diodes including a light conversion layer which converts received light to light with different wavelength.
2. Description of the Related Art
A white LED using a semiconductor, having advantages such as a long lifetime, capability of reduced size and operability at low voltage, is receiving attention as a next-generation LED.
There has been proposed a conventional technique of realizing white light by applying red, green and blue phosphors around a UV short wavelength LED. In this configuration, the red, green and blue phosphors are excited by the UV LED, and thus emit red, green and blue light, respectively. The red, green and blue light then mixes to produce white light.
However, there are a limited number of conventional phosphors that have sufficient light conversion efficiencies. The emission spectrum of these phosphors is not easily changed. Futhermore, the spectra are less than ideal in that the amount of light emitted varies as a function of wavelength. Hence, even by combining several phosphors, an optimum white light source is not obtained.
“Quantum dot” (QD) phosphors are phosphors whose emission spectra depends on the size of the particles, and hence can be used to convert light to a predetermined wavelength by utilizing the appropriate sized particles. Quantum dots are nanometer-sized semiconducting materials which exhibit quantum confinement effects. When the quantum dots are irradiated by light from an excitation source to reach energy excitation states, they emit energies corresponding to the respective energy band gaps. Since the control over the size of the quantum dots effectively controls the corresponding band gaps, energies of various wavelength regions can be obtained. QD phosphor is generally used in the form of resin mixture. Ligands are usually attached to the outer surface of the QD for high stability and high dispersion.
However, resin typically used for QD is optimized for inorganic phosphors. Since ligands conjugated with the outer surface of the QD are organic substances, resin interacts with the ligands, thereby hampering efficiency and durability of QD phosphors.